Medical catheters are formed of biocompatible material, and are constructed of a size and shape so they may be introduced into the human body without causing excessive trauma, their function being to transmit a liquid to or from a body cavity or organ.
Conventional medical catheters are roughly divided into two groups; metal catheters of high rigidity and rubber catheters of flexibility. Since both catheters have advantages and disadvantages for medical use, it is said that there is no catheter meeting fully the various delicate requirements of eliminating retained fluids from body cavities and organs, introducing medicinal solutions into the cavities and organs, eliminating the contents from gastro-intestinal, esophageal and tracheal tracts, or introducing some substances into the tracts.
The most important thing in the medical use of catheters is to avoid bacterial infections, and for this purpose, either boiling-sterilization (100.degree. C.) or steam-sterilization in an autoclave (121.degree. C.) is usually carried out before using catheters. Consequently, heat-stability at temperatures of, at least, 100.degree.-130.degree. C. is required for the catheter. Since catheters are inserted into the living body, their hardness should not be so high as to cause stimulation to the tissues which is subsequently followed by inflammation. But some degree of hardness is required for enabling the fluids or liquids to pass smoothly when some retained body fluids are eliminated from the body or when some medicinal solutions are introduced into the body. In addition, chemical resistance to the fluids and medicinal solutions is also required for the catheter.
As described above, miscellaneous specific properties are required for catheters but most of the catheters available are still made from natural rubber. Although the catheter made from natural rubber is excellent in flexibility, it lacks resistance to heat and chemicals. Thus, use of such a catheter has occasionally caused such troubles as swelling and dissolution of the catheter itself by the body fluids and medicinal solutions, extraction of the additives from the catheter by these fluids and solutions, aging of the catheter by sterilization and during storage as well as striking changes in elasticity, flexibility and tensile strength. It is said that this type of catheter is not a perfect catheter for medical use, having the drawbacks as above.
There are various other kinds of catheters, which are made from silicone rubber, butyl rubber, polychloroprene, polyvinyl chloride, polyethylene and polytetrafluoroethylene, in addition to the catheters made from natural rubber. However, there have been found no catheters to satisfy all the requirement including flexibility, hardness, heat-stability, resistance to body fluids and chemicals.
In particular, there have not been found any catheters suitable for introducing the gallstone solubilizer, which have been developed by the present inventors, directly into the biliary system.